The present invention relates to a vehicle steering system which enables an automatic steering control.
Techniques have been proposed in which a vehicle is automatically steered by making use of a steering actuator installed on the vehicle. For example, a power steering system installed on a vehicle includes an electric motor or a hydraulic actuator as a steering actuator for giving a steering force (a steering assist force) to a steering mechanism. By controlling outputs of these steering actuators, steered road wheels of the vehicle can be turned without relying on the steering operation by the driver.
More specifically, in an automatic parking control, a target traveling path from a current position of the subject vehicle to a parking position is operated, and a relationship of a target steering angle relative to a traveling distance of the vehicle is obtained in such a way that the vehicle can be reversed along the target traveling path so operated. Then, the steering actuator is controlled in such a way as to attain a target steering angle according to the traveling distance of the vehicle. As this occurs, the driver only has to adjust the vehicle speed and control a stopping position by applying the brakes and controlling the accelerator and does not have to perform the steering operation.
Of course, when an obstacle such as a person or other moving object enters the target traveling path after the automatic parking control has been started, the driver can intervene in the automatic parking control by not only applying the brakes but also applying an operating torque to a steering wheel. As this occurs, when it is detected that the operating torque applied to the steering wheel has surpassed a predetermined torque threshold, the automatic parking control is cancelled (JP-A-2004-284530).
In addition, there is also proposed a technique in which an automatic parking control is cancelled when the driver operates the steering wheel or releases his or her foot from the brake pedal during automatic parking control. Namely, when there is an intervention in the automatic parking control by the driver operating the devices, the automatic parking control is cancelled without any delay (JP-A-10-114272).
On the other hand, there is also proposed a technique in which an intervention by the driver operating the devices is permitted during automatic parking control, and when there is caused a fear that the operation by the driver brings the vehicle into contact with an obstacle, a control is performed which makes it difficult for the operation attempted by the driver to occur (JP-A-2006-21722).
In the conventional automatic parking controls, in general, the driver does not have to operate the steering wheel, and turning the steered road wheels of the vehicle is attained automatically by the steering actuator. Because of this, the driver is not placing his or her hands on the steering wheel during automatic parking control.
Nevertheless, also in the automatic parking control, the driving control which is similar to that executed during assist control is adopted conventionally as the driving control of the steering actuator, and from the viewpoints of making the control highly efficient and saving energy necessary for the control, there has been left a sufficient room for improvement.